A hybrid vehicle may include a driveline that operates in a plurality of modes to improve driveline efficiency. In one example, the hybrid driveline may include an engine, driveline disconnect clutch, and driveline integrated starter/generator (DISG). The engine and DISG may selectively provide torque to the hybrid driveline. In one mode, the engine may be decoupled from the DISG so that the DISG may propel the hybrid vehicle without having to expend energy rotating the engine when the engine is not combusting an air-fuel mixture and providing torque to the driveline (DISG only mode). In another mode, the engine may provide torque to propel the vehicle when the DISG is not providing torque to the driveline or absorbing torque from the driveline (engine only mode). In still another mode, the engine and DISG may both provide torque to propel the vehicle (DISG/engine mode). Thus, the hybrid driveline may operate in a plurality of modes based on vehicle operating conditions.
The same driveline modes may be made available when the hybrid vehicle is operating in a cruise or speed control mode. The vehicle may enter speed or cruise control mode when prompted to do so by a driver or a controller. The driver or controller selects a desired vehicle speed, and torque supplied to the vehicle's wheels is adjusted to maintain vehicle speed within a threshold speed of the desired speed. Actual vehicle speed as determined from output of a wheel speed sensor or driveline speed sensor may be used as feedback to control vehicle speed. The actual vehicle speed may be subtracted from the desired vehicle speed to determine a vehicle speed error. The vehicle speed error may be multiplied by a gain or controller transfer function to provide a driveline torque adjustment. The driveline torque adjustment may be output to the engine and/or the DISG which supply torque to the driveline so that vehicle speed converges to the desired vehicle speed.
Engine and/or DISG torque may be continuously adjusted to achieve the desired vehicle speed during speed control mode since driveline torque to maintain the desired vehicle speed may change with varying road conditions including road grade. Additionally, a driver or controller may adjust the desired vehicle speed depending on vehicle and/or road conditions. For example, a driver may reduce a desired vehicle speed while the vehicle is in speed or cruise control mode in response to entering a road construction zone. Similarly, the driver may increase the desired vehicle speed in response to exiting the road construction mode. The change in desired vehicle speed may initiate a change in engine and/or DISG requested torque so that the vehicle converges to a new desired vehicle speed. However, the change in requested driveline torque may initiate an engine stop or start (e.g., a change in driveline operating mode) that may be undesirable since the engine may be restarted only a short time after it is stopped to propel the vehicle at the new desired vehicle speed. Further, the driveline disconnect clutch may be opened and then closed shortly thereafter to change driveline operating modes and provide the desired new vehicle speed. Frequent changes in driveline modes (e.g., driveline mode change busyness) may reduce driveline durability and disturb the vehicle's passengers. For these reasons, it may be desirable to provide a method and system that may reduce driveline mode changes during a vehicle cruise or speed control mode.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method, comprising: during a closed-loop vehicle speed control mode, delaying a change in propulsion sources providing torque to a driveline or absorbing torque from the driveline in response to an amount of time since a change in a desired vehicle speed.
By delaying a driveline mode change in response to an amount of time since a change in a desired vehicle speed was initiated, it may be possible to provide the technical result of avoiding driveline mode change busyness that may be present in vehicle systems that use torque demand as a primary driveline mode change variable. For example, a driveline mode change may be delayed a predetermined amount of time since a change in desired vehicle speed. Consequently, even if there would be a large change in desired driveline torque, wheel torque, or transmission input shaft torque, the driveline may not immediately switch operating modes. Consequently, the driveline may switch between modes less often when the vehicle is operated in a closed-loop vehicle speed control mode.
The present description may provide several advantages. In particular, the approach may reduce the possibility of disturbing a driver due to frequent driveline mode changes. Additionally, the approach may reduce the possibility of driveline component degradation. Further, the approach may improve vehicle fuel economy via reducing unnecessary driveline mode changes. The described advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.